Of the numerous problems which have plagued boat enthusiasts, perhaps the most troublesome is that of controlling the attitude angle of the boat as it is moving through the water. This problem becomes especially acute with the use of outboard motors at the stern portion of the boat which tend to induce greater upward displacement of the bow during forward motion. Usually, during the early stages of acceleration, the bow of a boat will be at a fairly high angle relative to the water surface because of the degree of hull contact with the water and displacement of water from beneath the stern portion of the boat caused by rotation of the propeller. As the boat continues to accelerate, the amount of the hull in contact with the water decreases until the desired speed is reached, where in many cases, such as very high speed boating, only a small portion of the hull surface will be in contact with the water. At intermediate speeds as the boat is accelerating, porpoising is often a problem due to the boat not having reached an equilibrium state. Porpoising is both uncomfortable and dangerous because during this period of instability, other normally insignificant instabilities can be catalyzed or can combine to upset the boat causing possible injury to the occupants. This phenomena also has a detrimental effect on performance due to slapping of the hull against the water which increases the frictional resistance to forward movement. Also, the plane of rotation of the propeller is altered in an undesirable manner causing a significant loss in efficiency. It has been found that porpoising can be a problem in speeds ranging from about 10 up to about 50 miles per hour. At higher speeds, most high performance boats reach a planing attitude angle with only a very small portion of the hull surface in contact with the water, and only the propeller portion of the outboard motor beneath the surface of the water.
Other problems resulting from the use of outboard motors relate to the attitude angle of the boat as it is moving through the water in a general sense, as distinguished from the porpoising problem. Various devices have been fashioned to create a lift at the stern portion of the boat to alter an otherwise undesirable attitude angle. These devices have generally involved altered designs for the lower drive unit of the outboard motor. One such device is disclosed in U.S. Pat. No. 4,487,152 to Larson which illustrates the use of an air foil-shaped stabilizer above the propeller to induce a lift at the stern portion of the boat. An attitude control device in the form of a wing or vane is also disclosed in U.S. Pat. No. 3,980,035 to Johansson which shows the vane positioned in the slip stream behind the propeller. Other developments involve forming the anti-cavitation plate with an inclined lower surface to preclude formation of low pressure areas into which air or exhaust gases can be sucked, and to exert a lift at the stern of the boat. A deflector has also been developed to create a high pressure area at the trailing edge of the anti-cavitation plate to improve trim tab effectiveness by forestalling the passage of air into the area of the trim tab, such as the device disclosed by Holterman in U.S. Pat. No. 3,955,527. Of the patents noted above, only Larson suggests a function of controlling porpoising by using an air foil-type stabilizer above the propeller in the position normally assumed by the anti-cavitation plate.
Another problem alluded to above has been addressed by the use of trim tabs. These devices are ordinarily designed to counteract steering torque, i.e., the tendency of the boat to rotate due to the torque applied by the rotating propeller in the water which results in an undesirable steering effect. In most modern outboard engines, the trim trap is located vertically above and rearwardly of the propeller and consists of a fin-shaped member projecting downwardly into the upper part of the slip stream following the propeller. A primary effect of the trim tab is to produce a torque in counteraction to the steering torque so that the boat responds in a balanced manner while making turns. Many such trim tabs are adjustably mounted to the lower surface of the anti-cavitation plate, usually by means of a disk-shaped support which can be rotated to alter the disposition of the trim tab depending on the boat style, water temperature, etc., to achieve the desired effect.
While the prior art includes trim tabs, inclined anti-cavitation plates, and various arrangements for inducing a lift at the rear of the boat, there exists a lack of a stabilizer which incorporates features adapted to address these various problems in a single, easily replaceable device of which a number can be manufactured having graduated sizes for custom fitting a boat to achieve optimum performance. While trim tabs have been easily replaceable, anti-cavitation plates have not. Thus, inclining the anti-cavitation plate or incorporating some other feature thereon to induce a lift at the rearward portion of the boat has been an essentially permanent modification to the outboard motor. This makes it difficult or impossible to switch motors from one boat to the other, as is the practice with many high speed boat enthusiasts.
Accordingly, there is a need for an easily replaceable stabilizer having features adapted to counteract both the steering torque phenomenon and for substantially eliminating porpoising of the boat, and which can be easily manufactured in a number of different forms to accommodate varying use patterns.
The present invention meets this need and therefore solves the foregoing and other problems long associated with high performance boats using outboard motors through provision of a stabilizer adapted to effect steering torque compensation and for substantially eliminating porpoising, which can be adjustably mounted due to the need for a trim tab adjustment, and easily interchangeable with other such devices of varying size so that the optimum stabilizing effect can be achieved.